Man-made computing devices at the molecular level have been described in the prior art. In the prior art, the basic computing elements are individual molecules or assemblies of active groups on the scale of 10 to 50 .ANG.. The "state" of such a molecular element is changed by altering the conformation of a given molecule, or by the addition (or subtraction) of an electron or a small chemical group.
There are several chief motivating ideas behind this literature. First, since molecular computation takes place (molecular biology is really a form of computation at the molecular level), it might be possible to build "electronic" or non-biological computational devices at the molecular level. Second, at the molecular level, one can understand how to build "p-n junctions", "photojunctions", "wires", and even "field-effect transistors"; thus, all the essential elements of VLSI (very large scale integration) technology appear to be present on the molecular scale. Third, both the realities of molecular biology and the theory of computation explain how to do essentially error-free computation with error-prone or erroneously constructed devices. Thus, the inevitable errors of construction, and the "noise" and errors which will be present when the size of computing energies is decreased towards .about.50 kT per decision (instead of the present .about.10.sup.6 kT per decision), need not in principle cause errors in the overall computation done by such devices. These ideas suggest building a molecularly based chip having a device density thousands of times larger than conventional VLSI (very large scale integrated) chips.
While molecular shift registers based on electron transfer have been disclosed and claimed in the above-mentioned Ser. No. 07/221,021, molecular systems for the implementation of such shift registers is required.